أَسْتَغْفِرُ اللَّهَ وَأَتُوبُ إِلَيْهِ
Transliteration
Astaghfirullaha wa atubu ilayh
English meaning
I seek the forgiveness of Allah and repent to Him.
When is it recited?
Recited 100 times daily.
Its virtue
The Prophet (PBUH) used to seek forgiveness 100 times a day.
Source
Bukhari, Da'awat 3, 6307; Muslim, Dhikr 41, 2702